The fluorescent light diffuser that dsankt suggested didn't work out too well for me. It definitely diffused the light, but I guess the specific type I used cast a nasty hot ring.. it made the light look like it was coming through a bee hive. It was also very fragile, so cutting it was a pain in the ass.
So, I tried the wax paper.. it's definitely the best I've found so far.
(Please ignore my UK-inspired consumerist ways that forced me at gun point to buy a BD Sidewinder) The wax paper is taped on with hockey tape. It works great, however.. wax paper apparently despises water.. hence you see tearing around the edges where it was splashed with water on various adventures. I keep tape and a roll of wax paper in my trunk, and spend 5 minutes re-doing my lights time to time.
The light is pretty soft, and never gets hotspots.. but my light doesn't carry the same power as a Garrity (it's a bit less, but lasts about an hour after a 24 hour charge).. it's bulky and awkward, so I keep it slinged around me.